Well packers are used to create seals in downhole environments. Typically, a well packer is used to form a seal in the annular space between a casing and a tubular located in the casing or between a drilled hole and a tubular located in the drilled hole. Instead of mechanical or inflatable well packers, it is known to form well packers from a material that swells upon contact with hydrocarbons present in the downhole environment. Examples of hydrocarbon swellable materials include natural and synthetic elastomers such as ethylene propylene diene monomer (EPDM) rubbers. Examples of hydrocarbon swellable packers and suitable materials are described in GB 2411918.
In certain applications it is desirable to have a well packer that swells on exposure to hydrocarbons and water. Such well packers comprise material that is capable of swelling upon contact with hydrocarbons and material that is capable of swelling upon contact with water or brine. Such materials may be referred to as “hybrid” swelling materials. A well packer that swells upon contact with both hydrocarbons and water may provide for a proper seal during both the initial and the subsequent stages of production. During an early stage of production the production fluid may be comprised essentially of hydrocarbons and during later stages of production the water content of the production fluid may increase.
WO 05/012686 discloses a swellable material for downhole applications comprising an elastomeric matrix material to which has been added super absorbent polymer (SAP) particles. Such SAP particles can be classified into starch systems, cellulose systems and synthetic resin systems. The SAPs have hydrophilic characteristics by virtue of the presence of alcohols, carboxylic acids, amides or sulphuric acids. Cross-linking between the particles creates a three dimensional network. A compound is mixed with and bound to the material to maintain the desired diffusion gradient and allow for continued absorption of water (and thus continued swelling) in aqueous conditions.
US 2007/0027245 discloses oilfield elements and assemblies comprising elastomeric compositions capable of swelling in oil and water. The compositions comprise the reaction product of linear or branched polymers having residual ethylenic unsaturation with an unsaturated organic monomer having at least one acidic reactive moiety.
The present inventor has appreciated certain shortcomings of known well packers formed of material capable of swelling upon contact with hydrocarbons and water. In particular, swelling of hybrid materials may be inadequate or slow in aqueous (water or brine) conditions.